Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of leaks that could release fuel vapors to the atmosphere. In a typical leak test, a vacuum is applied to the fuel system. The integrity of the system is determined by monitoring the decay of the applied vacuum or by comparing the resulting fuel system pressure to an expected pressure. The vacuum source may be the intake manifold of the vehicle engine.
In some vehicles, such as hybrid electric vehicles, the vehicle engine may not run frequently, or may not generate enough vacuum to conduct a leak test. Such vehicles are required to have an evaporative leak check module (ELCM) coupled to the fuel system. The ELCM includes a vacuum pump that can be coupled to the fuel system for leak testing. A typical ELCM also contains a reference orifice. As a reference check, the ELCM may be isolated from the fuel system, and the vacuum pump activated to draw a vacuum on the reference orifice. The resulting pressure serves as a reference for leaks of equivalent size. The ELCM can then be coupled to the fuel system, and the vacuum pump activated. If the system is intact, the reference vacuum should be attained.
However, evolving regulations require testing for different size leaks in different sectors of the fuel system. For example, plug-in hybrid electric vehicles (PHEVs) will be required to test for 0.01″ leaks in the fuel tank and 0.02″ leaks in the rest of the system. The most common ELCM used in auto manufacturing includes a 0.02″ reference orifice. This is inadequate to test for 0.01″ leaks using above described method. Adding an additional reference orifice and associated valves would be costly. Further, vehicles currently in production will be unable to meet future standards as they are currently equipped.
The inventors herein have recognized these problems, and have developed systems and methods to at least partially address them. In one example a method, comprising: indicating a leak of a first diameter on a canister side of a fuel system following applying a vacuum to the fuel system with a fuel tank isolation valve closed; and indicating a leak of a second diameter on a fuel tank side of the fuel system, based on a vacuum decay in an isolated fuel tank following applying a vacuum to the fuel system with the fuel tank isolation valve open. In this way, an evaporative leak check module with a single reference orifice may be used to determine leaks of multiple sizes in multiple sectors of a fuel system. This may allow current vehicle production models to meet more stringent emissions regulations in the future.
In another example, a method for an evaporative emissions system leak test, comprising: determining a reference vacuum threshold; determining a first fuel system pressure by drawing a vacuum on a fuel system with a fuel tank isolation valve closed; indicating a leak of a first diameter based on a comparison of the first fuel system pressure to the reference vacuum threshold; opening the fuel tank isolation valve; drawing a vacuum on a fuel system with the fuel tank isolation valve open; closing the fuel tank isolation valve responsive to a second fuel system pressure reaching the reference vacuum threshold; monitoring a rate of change of a fuel tank vacuum while maintaining the fuel tank isolation valve closed; and indicating a leak based on the rate of change of the fuel tank vacuum. In this way, the fuel tank of a vehicle may be tested for leaks smaller than the reference orifice of an evaporative leak check module. This method will save costs associated with adding additional components to evaporative leak check modules to meet future emissions standards.
In another example, a fuel system for a vehicle, comprising: a fuel tank; a fuel vapor canister coupled to the fuel tank via a fuel tank isolation valve; an evaporative leak check module coupled to the fuel vapor canister via a canister vent valve; and a control system including executable instructions stored in non-transitory memory for: determining a reference vacuum threshold; determining a first fuel system pressure by drawing a vacuum on a fuel system with a fuel tank isolation valve closed; indicating a leak of a first diameter based on a comparison of the first fuel system pressure to the reference vacuum threshold; opening the fuel tank isolation valve; drawing a vacuum on a fuel system with the fuel tank isolation valve open; closing the fuel tank isolation valve responsive to a second fuel system pressure attaining the reference vacuum threshold; monitoring a rate of change of a fuel tank vacuum while maintaining the fuel tank isolation valve closed; and indicating a leak of a second diameter, smaller than the first diameter, based on the rate of change of the fuel tank vacuum. In this way, PHEV's may comply with emissions testing standards, without forcing the vehicle engine on to generate sufficient vacuum for evaporative leak testing, thus maintaining or improving the vehicle fuel economy benefits.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.